What is ambient occlusion?

How do we get this result in realtime?

Screen space ambient occlusion

Screen space ambient occlusion is the indrectional shadowing of the raw geometry of a scene. It's a screen space post processing effect of the engine, procedurally generated. The detail amount depents on the raw geometry.

Ambient occlusion map

With screen space ambient occlusion there are no indirect shadows in surface details. For that we need ambient occlusion information texture based. The resolution is an ambient occlusion map.